Retroviruses are small enveloped viruses that contain a diploid, single-stranded RNA genome, and replicate via a DNA intermediate produced by a virally-encoded reverse transcriptase, an RNA-dependent DNA polymerase. Retroviruses include, for example, oncogenic viruses such as human T-cell leukemia viruses (HTLV-I, -II, -III), and feline leukemia virus as well as Human Immunodeficiency Virus (HIV-1 and HIV-2). HIV-1 is a member of the lentivirus family of retroviruses which contains a single-stranded RNA genome and is considered the major etiological agent involved in the development of acquired immunodeficiency syndrome (AIDS) and related disorders. The World Health Organization (WHO) estimates that as of the end of 2007 over 42 million people worldwide are infected and this number is growing. A great deal of effort to develop drugs against HIV has been centered around HIV reverse transcriptase (RT), HIV protease, and more recently viral entry.
Numerous gene therapy clinical trials for the treatment of AIDS have been undertaken yielding mostly disappointing results, both in terms of viral load and of CD4+ T cells counts (Rossi, J. J., et al., 2007. Nat Biotechnol 25:1444-54). In particular, while it is desirable that transgene-expressing cells survive and proliferate in the recipient patients, the opposite is often seen. For instance, following gene transfer of an anti-HIV ribozyme in hematopoietic stem cells, a 5-fold reduction in expression of the ribozyme was observed within 6 months (Mitsuyasu, R. T. et al., 2009. Nat Med 15:285-92). Rapid elimination of productively HIV-1-infected lymphocytes is well-known (Coffin, J. M., 1995. Science 267:483-9.) and results from the action of cytotoxic T lymphocytes (CTLs) and also from virus-related apoptosis.
None of the current AIDS treatments have proven to be totally effective in treating and/or reversing the disease. In addition, many of the compounds currently used to treat AIDS cause adverse side effects including low platelet count, renal toxicity and bone marrow cytopenia.
Thus, there continues to be a significant need for new therapeutic strategies for retroviral infections such as HIV infection and associated conditions such as AIDS.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.